In the field of integrated circuit ("IC") fabrication, one type of integrated circuits are typically fabricated on a single wafer of semiconductor substrate. Typically, the semiconductor wafer is a thin, flat and substantially circular disk of semiconducting material. The semiconductor wafer is typically from 4 to 8 inches in diameter. The wafer typically goes through a number of manufacturing phases in order to make the integrated circuits. The manufacturing phases typically include initial preparation, processing and testing.
The initial preparation typically includes steps of designing circuits, laying out the designed circuits, preparing photomasks in accordance with the circuit layout, and preparing the wafer for processing. The processing typically includes different diffusion processes to fabricate the integrated circuits. Each processing step typically employs one or more photomasks. The integrated circuits are thus fabricated on the processed wafer. The processed wafer then goes through various testing procedures.
The processing of the wafer typically require various semiconductor wafer processing equipment. The various wafer processing machines are typically separately located and the wafer being processed are typically transported from one machine to another machine by means of a wafer cassette. A wafer cassette can typically hold a number of wafers. Typically, the wafer cassette is located on a particular wafer processing machine to collect the wafers being processed by that machine. When the wafer cassette is full, the wafer cassette is removed from the machine and is transported to a next machine such that the wafers contained in the wafer cassette can receive further processing. The wafer cassette is typically mounted on the platform of the machine to supply and/or collect wafers.
The wafer cassette is typically required to be secured within a predefined target area on the platform of a wafer processing equipment such that the equipment can receive the wafers contained in the wafer cassette or forward the processed wafers to the wafer cassette. In order to secure the wafer cassette within the predefined target area on the platform, various prior art arrangements and devices have been developed. One type of prior art arrangement for securing a wafer cassette on a platform at a predefined area is illustrated in FIGS. 1 and 2.
Referring to FIGS. 1 and 2, a wafer cassette 11 is shown which is to be loaded on a wafer cassette holder 12 mounted on a platform 14 of a wafer processing equipment (not shown). FIG. 1 only shows a portion of platform 14. Wafer cassette 11 holds a number of wafers 11a through 11n. Wafer cassette 11 also includes an H-shaped bar 18 at its bottom (shown in FIG. 2). As shown in FIG. 2, H-shaped bar 18 includes two vertical bars 18a and 18b and a lateral bar 18c mounted between two vertical bars 18a and 18b.
Wafer cassette holder 12 includes two locking members 12a and 12b mounted on platform 14. Locking members 12a-12b of wafer cassette holder 12 are mounted separately platform 14 to define the predefined target area within which wafer cassette 11 is secured on platform 14. Wafer cassette 11 typically loaded on locking members 12a-12b of wafer cassette holder 12 and is secured by cassette holder 12.
Locking member 12a of wafer cassette holder 12 includes a base bar 16 that is mounted on platform 14. Locking member 12b includes a base bar 17 that is mounted on platform 14. When wafer cassette 11 is loaded on wafer cassette holder 12, each vertical bars 18a-18b of H-shaped bar 18 contacts the top surface of one of base bar 16 and 17, respectively, as shown in FIG. 1.
Locking member 12a of wafer cassette holder 12 further includes two tabs 20a and 20b located on the top surface of base bar 16. Tabs 20a-20b are spaced apart to define a notch 22 in between. Likewise, locking member 12b includes two tabs 21a and 21b located on the top surface of base bar 17. Tabs 21a-21b are spaced apart to define a notch 23 in between. The function of tabs 20a-20b and 21a-21b and notches 22-23 is to secure wafer cassette 11 on base bars 16-17, and therefore on platform 14, without horizontal movement. When wafer cassette 11 is located on wafer cassette holder 12, notches 22 and 23 are occupied by lateral bar 18c of H-shaped bar 18. When lateral bar 18c is clamped in notches 22 and 23, each vertical bars 18a-18b is held against one of two sets of tabs 20a-20b and 21a-21b , respectively. This cause H-shaped bar 18 to be free from any horizontal movement which, in turn, securely locks wafer cassette 11 on wafer cassette holder 12 without horizontal movement.
Disadvantages are, however, associated with this prior approach. One disadvantage associated is that a very small positional displacement of the wafer cassette is allowed during the loading of the wafer cassette on the wafer cassette holder. In order to lock the wafer cassette on the wafer cassette holder, the lateral bar of the H-shaped bar needs to be precisely aligned with the notches when the wafer cassette is loaded. The precise alignment of the lateral bar with the notches during the cassette loading typically requires manual operation by human operators. This typically increases the loading time of the wafer cassette which, in turn, reduces the total throughput of the processing equipment. In addition, the manual loading of the wafer cassette creates ergonomics problems.
Moreover, the precise alignment of the lateral bar with the notches during the cassette loading typically increases the cost to automate the loading of the wafer cassette. When loading and unloading of the wafer cassette is done automatically by a robotical arm, the robotical arm is required to have a high degree of accuracy. This typically increases the manufacturing cost of the robotical arm.